Method of delivering a PDCP data unit to an upper layer

ABSTRACT

Disclosed is a radio (wireless) communication system providing a radio communication service and a terminal, and more particularly, to a method of delivering a continuously and/or consecutively received Packet Data Convergence Protocol (PDCP) Service Data units (SDUs) to an upper layer immediately if a PDCP entity receives the PDCP SDUs during a process of a RLC re-establishment within an Evolved Universal Mobile Telecommunications System (E-UMTS) that has evolved from a Universal Mobile Telecommunications System (UMTS) or a Long Term Evolution (LTE) system.

CROSS-REFERENCE

The present application claims priority benefit to the followingapplications, which contents are all incorporated by reference for allpurposes as if fully set forth herein: U.S. Provisional Application Nos.61/074,233 (filed Jun. 20, 2008), 61/074,998 (filed Jun. 23, 2008),Korean Application No. 10-2009-0050624 (filed Jun. 8, 2009), UnitedKingdom Patent Application No. 0910196.5 (filed Jun. 12, 2009).

TECHNICAL FIELD

The present invention relates to a radio (wireless) communication systemproviding a radio communication service and a terminal, and moreparticularly, to a method of delivering a Packet Data ConvergenceProtocol (PDCP) Service Data unit (SDU) to an upper layer within areceiving side entity of an Evolved Universal Mobile TelecommunicationsSystem (E-UMTS) that has evolved from a Universal MobileTelecommunications System (UMTS) or a Long Term Evolution (LTE) system.

BACKGROUND ART

FIG. 1 shows an exemplary network structure of a Long-Term Evolution(LTE) system as a mobile communication system to which a related art andthe present invention are applied. The LTE system is a system that hasevolved from the existing UMTS system, and its standardization work iscurrently being performed by the 3GPP standards organization.

The LTE network can roughly be divided into an Evolved UMTS TerrestrialRadio Access Network (E-UTRAN) and a Core Network (CN). The E-UTRAN isgenerally comprised of a terminal (i.e., User Equipment (UE)), a basestation (i.e., Evolved Node B (eNode B)), an access gateway (aGW) thatis located at an end of the network and connects with one or moreexternal networks. The access gateway may be divided into a part thathandles processing of user traffic and a part that handles controltraffic. In this case, the access gateway part that processes the usertraffic and the access gateway part that processes the control trafficmay communicate with a new interface. One or more cells may exist in asingle eNB. An interface may be used for transmitting user traffic orcontrol traffic between eNBs. The CN may include the aGW and a node orthe like for user registration of the UE. An interface fordiscriminating the E-UTRAN and the CN may be used.

FIGS. 2 and 3 show respective exemplary structures of a radio interfaceprotocol between the terminal and the E-UTRAN based on the 3GPP radioaccess network standards. The radio interface protocol has horizontallayers comprising a physical layer, a data link layer, and a networklayer, and has vertical planes comprising a user plane (U-plane) fortransmitting user data information and a control plane (C-plane) fortransmitting control signaling. The protocol layers in FIGS. 2 and 3 canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on three lower layers of an open system interconnection(OSI) standard model widely known in the communication system. The radioprotocol layers exist as pairs between the UE and the E-UTRAN and handlea data transmission in a radio interface.

The layers of the radio protocol control plane in FIG. 2 and those ofthe radio protocol user plane in FIG. 3 will be described as follows.

The physical layer, the first layer, provides an information transferservice to an upper layer by using a physical channel. The physicallayer is connected to an upper layer called a medium access control(MAC) layer via a transport channel. Data is transferred between the MAClayer and the physical layer via the transport channel. The transportchannel is divided into a dedicated transport channel and a commontransport channel according to whether or not a channel is shared.Between different physical layers, namely, between a physical layer of atransmitting side and that of a receiving side, data is transmitted viathe physical channel using radio resources.

The second layer includes various layers. First, a medium access control(MAC) layer performs mapping various logical channels to varioustransport channels and performs logical channel multiplexing by mappingseveral logical channels to a single transport channel. The MAC layer isconnected to an upper layer called a radio link control (RLC) layer by alogical channel. The logical channel is roughly divided into a controlchannel that transmits information of the control plane and a trafficchannel that transmits information of the user plane according to a typeof transmitted information.

A Radio Link Control (RLC) layer of the second layer segments and/orconcatenates data received from an upper layer to adjust the data sizeso as for a lower layer to suitably transmit the data to a radiointerface. In addition, in order to guarantee various Quality ofServices (QoSs) required by each radio bearer (RB), the RLC layerprovides three operational modes: a Transparent Mode (TM); anUnacknowledged Mode (UM); and an Acknowledged Mode (AM). In particular,the AM RLC performs a retransmission function through an AutomaticRepeat and Request (ARQ) for a reliable data transmission.

A Packet Data Convergence Protocol (PDCP) layer of the second layerperforms a function called header compression that reduces the size of aheader of an IP packet, which is relatively large and includesunnecessary control information, in order to effectively transmit the IPpacket such as an IPv4 or IPv6 in a radio interface having a narrowbandwidth. The header compression increases transmission efficiencybetween radio interfaces by allowing the header part of the data totransmit only the essential information. In addition, the PDCP layerperforms a security function in the LTE system. The security functionincludes ciphering for preventing data wiretapping by a third party, andintegrity protection for preventing data manipulation by a third party.

The Radio Resource Control (RRC) layer located at the lowermost portionof the third layer is defined only in the control plane, and controls alogical channel, a transport channel and a physical channel in relationto the configuration, reconfiguration, and release of radio bearers(RBs). In this case, the RBs refer to a logical path provided by thefirst and second layers of the radio protocol for data transmissionbetween the UE and the UTRAN. In general, configuration (establishment,setup) of the RB refers to the process of stipulating thecharacteristics of a radio protocol layer and a channel required forproviding a particular data service, and setting the respective detailedparameters and operational methods. The RBs include two types: aSignaling RB (SRB) and a Data RB (DRB). The SRB is used as a path fortransmitting an RRC message on a C-plane, and the DRB is used as a pathfor transmitting user data on a U-plane.

In the related art, for a PDCP SDUs received through a RLC (Radio LinkControl) re-establishment, a PDCP entity of a receiving side performs areordering process after storing the PDCP SDU in a buffer withoutdelivering the received PDCP SDUs to an upper layer. Those stored PDCPSDUs in the buffer are only delivered to the upper layer upon acomparison result of its sequence numbers (SN) with sequence numbers ofnew PDCP SDUs that are received after the RLC re-establishment.

In related art, a retransmission of PDCP SDUs by the PDCP entity intransmitting side is based on a RLC status report rather than the RLCre-establishment. As such, in often cases, the PDCP may receive allmissing PDCP SDUs through exceed number of the RLC re-establishment. Forexample, if a plurality of handovers is occurred in a limited timeperiod, a possibility for reception of the all missing PDCP SDUs is veryhigh, as the plurality of handovers causes a plurality of RLCre-establishments. However, repeatedly re-transmitting the missing PDCPSDUs during the plurality of RLC re-establishments may cause anunnecessary time delay or a waste of radio resources.

Also, as explained above, those PDCP SDUs received through the RLCre-establishment are not delivered to the upper layer immediately.Rather, a reordering process is performed for those PDCP SDUs afterstoring them in the buffer. This may cause an unnecessary time delay aswell. In addition, a deadlock situation may happen in case that a PDCPSDU received through the RLC re-establishment is a last packet of a datastream. For example, if the PCDP SDU is the last packet of the datastream, since there are no more data to be received through the RLCre-establishment, such PDCP SDU is continuously kept in the bufferinstead of delivering to the upper layer.

Therefore, there is a need to have a solution for the aforementioneddrawbacks of the related art.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to minimize a timedelay of data transmission, to prevent a waste of radio resources duringthe data transmission, and/or to prevent a deadlock situation during adelivery of PDCP SDUs to an upper layer.

For this, the present invention proposes to deliver a continuouslyand/or consecutively received PDCP SDUs to the upper layer immediatelyif a PDCP entity receives the PDCP SDUs from a RLC entity through a RLCre-establishment.

To achieve this and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a data communication method in a wirelesscommunication system, the method comprising: receiving a data unithaving a sequence number from a lower layer; storing the received dataunit in a buffer; determining whether the sequence number of thereceived data unit is equal to a sequence number +1 from a sequencenumber of a last delivered data unit; and delivering all stored dataunits with consecutively associated sequence numbers greater than orequal to the sequence number of the received data unit in ascendingorder of the associated sequence number based on the determining step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary network structure of an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) as a mobile communicationsystem to which a related art and the present invention are applied;

FIG. 2 is an exemplary view of related art control plane architecture ofa radio interface protocol between a terminal and an E-UTRAN;

FIG. 3 is an exemplary view of related art user plane architecture of aradio interface protocol between a terminal and an E-UTRAN;

FIG. 4 is an exemplary structure of a PDCP entity to which the presentinvention is applied;

FIG. 5 is an exemplary data flow representing a delivery of PDCP dataunit;

FIG. 6 is an exemplary data flow representing a reordering and adelivery of PDCP data unit;

FIG. 7 is an another exemplary data flow representing a reordering and adelivery of PDCP data unit;

FIG. 8 is a first exemplary data flow representing a delivery of PDCPdata unit according to the present invention; and

FIG. 9 is a second exemplary data flow representing a delivery of PDCPdata unit according to the present invention.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

One aspect of this disclosure relates to the recognition by the presentinventors about the problems of the related art as described above, andfurther explained hereafter. Based upon this recognition, the featuresof this disclosure have been developed.

Although this disclosure is shown to be implemented in a mobilecommunication system, such as a UMTS developed under 3GPPspecifications, this disclosure may also be applied to othercommunication systems operating in conformity with different standardsand specifications.

Hereinafter, description of structures and operations of the preferredembodiments according to the present invention will be given withreference to the accompanying drawings.

As described above, the present invention aims to minimize a time delayof data transmission, to prevent a waste of radio resources during thedata transmission, and/or to prevent a deadlock situation during adelivery of PDCP SDUs to an upper layer.

To this end, the present invention proposes to deliver a continuouslyand/or consecutively received PDCP SDUs to the upper layer immediatelyif a PDCP entity receives the PDCP SDUs from a RLC entity by a RLCre-establishment.

A detailed description of a PDCP entity will be given as following. Ingeneral, the PDCP entity is connected with a RRC layer or a userapplication in upward, and is connected with a RLC layer in downward.FIG. 4 is an exemplary structure of a PDCP entity to which the presentinvention is applied. As illustrated in FIG. 4, the PDCP entity isdivided into a PDCP transmitting side and a PDCP receiving side. A PDCPentity in a transmitting side transmits service data units (SDUs) andprotocol data unit (PDU) to a peer PDCP entity in a receiving side. APDCP entity in the receiving side extracts a PDCP SDU or controlinformation from the transmitted PDCP PDU. In general, a data PDU (PDCPdata PDU) and a control PDU (PDCP control PDU) are generated by the PDCPentity in the transmitting side. The data PDU is a data block that isgenerated in the PDCP by processing the received SDU from an upper layerof the PDCP entity, and the control PDU is a data block that isgenerated in the PDCP for providing control information to a peerentity. The PDCP data PDU is generated in both user plane and controlplane of a radio bearer (RB). Some functions of the PDCP are selectivelyapplied for each of user and control plane. For example, a headercompression function is only applied to data in the user plane, and anintegrity protection function of a security function is only applied todata in the control plane. The security function also includes aciphering function for data, and the ciphering function is applied todata in both user and control plane. The PDCP control PDU may be used toindicate a PDCP reception buffer status (i.e. a PDCP status report)and/or to indicate a status of header decompression (i.e., a headercompression feedback packet).

The data processing procedure operated in a PDCP transmitting side willbe given as following. First, the PDCP layer (or entity) stores areceived PDCP SDU in a transmission buffer, and assigns a sequencenumber (SN) for each of PDCP SDU. (S1) If a setting radio bearer is adata radio bearer (DRB) (i.e., radio bearer of user plane), the PDCPlayer performs a header compression with respect to the PDCP SDU. (S2)If a setting radio bearer is a signaling radio bearer (SRB) (i.e., radiobearer of control plane), the PDCP layer performs an integrityprotection operation with respect to the PDCP SDU. (S3) After, withrespect to a data block generated by a result of S2 or S3, the PDCPlayer performs a ciphering. (S4) The PDCP generates a PDCP PDU by addinga header to the generated data block from S4, and then the PDCP deliverthe generated PDCP PDU to a RLC layer.

The data processing procedure operated in a PDCP receiving side will begiven as following. First, the PDCP layer (or entity) removes a headerform the received PDCP PDU. (S1) Thereafter, the PDCP layer performs adeciphering with respect to the PDCP PDU without the header. (S2) If asetting radio bearer is a data radio bearer (DRB) (i.e., radio bearer ofuser plane), the PDCP layer performs a header decompression with respectto the deciphered PDCP PDU. (S3) If a setting radio bearer is asignaling radio bearer (SRB) (i.e., radio bearer of control plane), thePDCP layer performs an integrity protection operation with respect tothe deciphered PDCP PDU. (S4) After the step of 3 or 4, the PDCP layerdelivers the processed data blocks (i.e., PDCP SDUs) to an upper layer.(S5) If the setting radio bearer is a data radio bearer (DRB) used in aradio link control acknowledged mode (RLC AM), the processed data blocksmay be stored in a reception buffer, and then may deliver to the upperlayer after performing an reordering operation. (S6) Here, if thesetting radio bearer is a data radio bearer (DRB) used in a radio linkcontrol acknowledged mode (RLC AM), the reordering operation must beperformed because the DRB used in the RLC AM usually transmits an errorsensitive data traffic. For this, a retransmission of data is performedto minimize data transmission errors during a wireless communication.The reordering operation is needed to deliver PDCP SDUs to the upperlayer in-sequence order. In RLC AM, many different ‘state variable’ canbe used to deliver the PDCP PDU to the upper layer in-sequence delivery.

First, the state variable can be defined as following.

-   -   RSN (Received Sequence Number): a sequence number (SN) of        received PDCP SDU    -   LAST (Last submitted PDCP SDU SN): a sequence number of last        delivered PDCP SDU among all delivered PDCP SDUs to the upper        layer    -   NEXT (Next expected PDCP SDU SN): a sequence number of a next        PDCP SDU of a PDCP SDU having a highest SN among all received        PDCP SDU (i.e., highest PDCP SDU SN+1)

Using the above state variable, when the PDCP entity in a receiving sidereceives a PDCP SDU, the PDCP entity may process a received PDCP SDU asfollowing procedure. Here, for exemplary purpose only, it is assumedthat all values are limited to a range of 0 to 4095 and a smallest valueis a NEXT-2048.

First, if the PDCP entity receives a PDCP SDU having a sequence numberthat is smaller or less than a sequence number of PDCP SDU previouslydelivered to an upper layer, the received PDCP SDU is discarded becauseit is an outdated PDCP SDU. This procedure can be expressed in aprocedure text as following.

-   -   if NEXT −2048<=RSN <=LAST        -   decipher        -   decompress        -   discard

If the PDCP entity receives a PDCP SDU having a sequence number that isbetween a SN of last delivered PDCP SDU to the upper layer and a SN of aPDCP SDU having a highest SN, the received PDCP SDU is discarded if itis a duplicated PDCP SDU. If it is not a duplicated PDCP SDU, thereceived PDCP SDU is stored in a reception buffer. This procedure can beexpressed in a procedure text as following.

-   -   if LAST<RSN<NEXT        -   decipher        -   decompress        -   if not duplicate, store in the reception buffer        -   if duplicate, discard

If the PDCP entity receives a PDCP SDU having a sequence number that isgreater than or equal to a sequence number of PDCP SDU having a highestSN, the received PDCP SDU is stored in the reception buffer because itis a new PDCP SDU. Then, the NEXT is updated to RSN+1. This procedurecan be expressed in a procedure text as following.

-   -   if NEXT <=RSN<NEXT+2048        -   decipher        -   decompress        -   store in the reception buffer        -   set NEXT to RSN+1

After processing and storing the received PDCP SDU using the aboveprocedure, the PDCP entity (or layer) may deliver the stored PDCP SDU toan upper layer using a following procedure. The following procedure canbe expressed in a procedure text as following.

-   -   if the PDCP SDU received by PDCP is not due to the RLC        re-establishment:        -   deliver to upper layer in ascending order of the associated            SN value:            -   all stored PDCP SDU(s) with an associated SN<RSN;            -   all stored PDCP SDU(s) with consecutively associated SN                value(s)>=RSN;        -   set LAST to the SN of the last PDCP SDU delivered to upper            layers.

Namely, the immediate delivery of PDCP SDUs to the upper layer is onlyperformed when the reception of the PDCP SDUs is not due to the RLCre-establishment. However, the reordering operation must be performedfor the received PDCP SDUs from the RLC re-establishment.

FIG. 5 is an exemplary data flow representing a delivery of PDCP dataunit. As illustrated in FIG. 5, firstly, a PDCP PDU containing a PDCPSUD with a sequence number is received. Here, the sequence number may bedefined as ‘RSN’. Thereafter, an operation of a deciphering and a headerdecompression are performed, and then the deciphered and decompressedPDCP SDU is stored in a PDCP buffer. Then, the PDCP entity check whethera RSN is greater than or equal to a NEXT. If the RSN is greater than orequal to the NEXT, the NEXT is set to RSN+1. Then, the PDCP entitydetermines that the received PDCP SDU is received due to the RLCre-establishment. If it is determined that the received PDCP SDU isreceived due to the RLC re-establishment, the delivery procedure of thePDCP SDU is terminated. If not, the PDCP entity delivers to upper layerall stored PDCP SDU(s) with an associated SN<RSN in ascending order ofthe associated SN value. Further, the PDCP entity also delivers to upperlayer all stored PDCP SDU(s) with consecutively associated SNvalue(s)>=RSN in ascending order of the associated SN value. Thereafter,the PDCP sets LAST to the SN of the last PDCP SDU delivered to the upperlayer, and terminates the PDCP SDU delivery procedure.

FIG. 6 is an exemplary data flow representing a reordering and adelivery of PDCP data unit. In order to provide simple explanation, inFIG. 6, a PDCP control PDU is not considered, and there is assumptionthat a single PDCP PDU is included in a single RLC PDU and the PDCP PDUincludes a single PDCP SDU.

First, a RLC entity in a receiving side consecutively (in-sequence)receives a RLC PDU up to RLC PDU=13, then delivers them to a PDCP entityin the receiving side. When the RLC PDUs are delivered to the PDCPentity, the receiving RLC entity notifies a RLC entity in a transmittingside about successful reception of RLC PDUs up to RLC PDU=13 through aRLC status report. A receiving PDCP entity may delivery to an upperlayer all PDCP SDU(s) up to PCDP SDU=22, as they were receivedin-sequence order. Here, a transmitting PDCP entity may be notified oracknowledged that a successful reception of PDCP SDUs up to PDCP SDU=22through the RLC status report.

As illustrated in FIG. 6, before the RCL re-establishment, thetransmitting RLC entity transmits the RLC PDU=14 to RLC PDU=20, but RLCPDU=16, 17, 19 fails to be transmitted. As such, the receiving RLCentity delivers to a PDCP entity of upper layer the in-sequence receivedRLC SN up to RLC SN=15, and the PDCP entity also delivers to its upperlayer the in-sequence received PDCP SDU up to PDCP SN=24. At this time,the LAST is equal to 24, and the NEXT is equal to 25. The RLC PDU=18 andRLC PDU=20 is successfully received, but these RLC PDUs are stored inthe reception buffer as some of previous RLC PDUs are not successfullyreceived. At this time, the receiving RLC entity has to notify this tothe transmitting RLC entity through the RLC status report, but the RLCre-establishment is happen before the transmission of the RLC statusreport. (S1)

If the RLC re-establishment is happen due to a handover, those RLC PDU,which have been successfully received but stored in the buffer becausesome of previous RLC PDUs are not received successfully, deliver to anupper layer of the PDCP entity. In case of the FIG. 6, the RLC PDU=18and RLC PDU=20 are applied in this situation, thusly the RLC PDU=18 andRLC PDU=20 are delivered to the upper layer accordingly. The PDCP entitystores a received PDCP SDU due to the RLC re-establishment in the PDCPreception buffer. As such, the PDCP SDU=27 and PDCP SDU=29 are stored inthe PDCP reception buffer. As the transmitting PDCP entity determines asuccessful PDCP SDU transmission result based on a most recent RLCstatus report, the transmitting PDCP entity concludes that the PDCP SDUsup to PDCP SDU=22 are successfully transmitted and the PDCP SDUs betweenPDCP SDU=23 and PDCP SDU=29 are not successfully transmitted. (S2)

After the RLC re-establishment, the RLC entity initializes or resets allstate variables, and restarts a data transmission. The transmitting PDCPentity may retransmit those PDCP SDUs that were not successfullytransmitted to the receiving PDCP entity before the RLCre-establishment. Here, some of the PDCP SDUs may be lost, and thetransmitting PDCP entity may only retransmit transmittable PDCP SDUsin-sequence order. The transmitting PDCP entity retransmits those PDCPSDUs, which were not successfully transmitted before the RLCre-establishment, based on the most latest RLC status report. In case ofthe FIG. 6, the transmitting PDCP entity retransmits the PDCP SDUs (PDCPSDU=23 to PDCP SDU=29). These PDCP SDUs are transmitted through RLCPDUs=0 to RLC PDUs=6. When these RLC PDUs (0-6) are received by thereceiving RLC entity, these RLC PDUs are delivered to the receiving PDCPentity in-sequence order. If these RLC PDUs are received by thereceiving PDCP entity, the PDCP SDU=23 and 24 are discarded because theSN of theses PDCP SDU are less than the LAST, and the PDCP SDU=27 and 29are also discarded because these PDCP SDUs are already stored. Thereceiving PDCP entity delivers to the upper layer from PDCP SDUs=25 toPDCP SDUs=29 in-sequence order. After delivering of the transmittablePDCP SDUs, the state variables of LAST and NEXT are updated as LAST=29and NEXT=30. (S3-1)

During the Handover, a source eNB may forward those unsuccessfullytransmitted PDCP SDUs to a target eNB. However, there is possibility ofdata loss at an interface between networks. In case of the FIG. 6, thePDCP SDUs (PDCP SDU=23 to PDCP SDU=29) were forwarded from the sourceeNB to the target eNB, but the PDCP SDUs from PDCP SDU=23 to PDCP SDU=27are lost during the RLC re-establishment. The transmitting PDPC entitytransmits the PDCP SDUs in ascending order (from PDCP SDU=28 to PDCPSDU=31) by including theses SDUs in the RLC PDUs (RLC PDU=0 to RLCPDU=3). If these RLC PDUs are received by the receiving PDCP entity,these RLC PDUs are delivered to the receiving PDCP entity in-sequenceorder. If these RLC PDUs are received by the receiving PDCP entity, thePDCP SDU=23 and 24 are discarded because the SN of theses PDCP SDU areless than the LAST, and the PDCP SDU=27 and 29 are also discardedbecause these PDCP SDUs are already stored. The receiving PDCP entitydelivers to the upper layer from PDCP SDUs=25 to PDCP SDUs=29in-sequence order. If the receiving PDCP receives PDCP SDU=28 includedin RLC PDU=0, the PDCP SDU=27 having smaller SN is delivered to theupper layer. Also, the PDCP SDU=28 and its consecutive PDCP SDU=29 alsoare delivered to the upper layer. After delivering of the transmittablePDCP SDUs, the state variables of LAST and NEXT are updated as LAST=29and NEXT=30. (S3-2)

FIG. 7 is an another exemplary data flow representing a reordering and adelivery of PDCP data unit;

First, a RLC entity in a receiving side consecutively (in-sequence)receives a RLC PDU up to RLC PDU=13, then delivers them to a PDCP entityin the receiving side. When the RLC PDUs are delivered to the PDCPentity, the receiving RLC entity notifies a RLC entity in a transmittingside about successful reception of RLC PDUs up to RLC PDU=13 through aRLC status report. A receiving PDCP entity may delivery to an upperlayer all PDCP SDU(s) up to PCDP SDU=22, as they were receivedin-sequence order. Here, a transmitting PDCP entity may be notified oracknowledged that a successful reception of PDCP SDUs up to PDCP SDU=22through the RLC status report.

As illustrated in FIG. 7, before the RCL re-establishment, thetransmitting RLC entity transmits the RLC PDU=14 to RLC PDU=20, but RLCPDU=16, 17, 19 fails to be transmitted. As such, the receiving RLCentity delivers to a PDCP entity of upper layer the in-sequence receivedRLC SN up to RLC SN=15, and the PDCP entity also delivers to its upperlayer the in-sequence received PDCP SDU up to PDCP SN=24. At this time,the LAST is equal to 24, and the NEXT is equal to 25. The RLC PDU=18 andRLC PDU=20 is successfully received, but these RLC PDUs are stored inthe reception buffer as some of previous RLC PDUs are not successfullyreceived. At this time, the receiving RLC entity has to notify this tothe transmitting RLC entity through the RLC status report, but the RLCre-establishment is happen before the transmission of the RLC statusreport. (S1)

If the RLC re-establishment is happen due to a handover, those RLC PDU,which have been successfully received but stored in the buffer becausesome of previous RLC PDUs are not received successfully, deliver to anupper layer of the PDCP entity. In case of the FIG. 7, the RLC PDU=18and RLC PDU=20 are applied in this situation, thusly the RLC PDU=18 andRLC PDU=20 are delivered to the upper layer accordingly. The PDCP entitystores a received PDCP SDU due to the RLC re-establishment in the PDCPreception buffer. As such, the PDCP SDU=27 and PDCP SDU=29 are stored inthe PDCP reception buffer. As the transmitting PDCP entity determines asuccessful PDCP SDU transmission result based on a most recent RLCstatus report, the transmitting PDCP entity concludes that the PDCP SDUsup to PDCP SDU=22 are successfully transmitted and the PDCP SDUs betweenPDCP SDU=23 and PDCP SDU=29 are not successfully transmitted. (S2)

After a first RLC re-establishment and before a second RLCre-establishment, the RLC PDUs (RLC PDUs=2-6 and 8) are stored in theRLC buffer due to missing RLC PDUs (S3)

At the second RLC re-establishment, the receiving PDCP entity mayreceive all missing PDCP SDUs (PDCP SDUs 25-29). However, these PDCPSDUs are not delivered to upper layer even if they are receivedin-sequence order, as illustrated in FIG. 7. (S4)

As explained above, an object of the present invention is to minimize atime delay of data transmission, to prevent a waste of radio resourcesduring the data transmission, and/or to prevent a deadlock situationduring a delivery of PDCP SDUs to an upper layer.

For this, the present invention proposes to use following procedure textfor delivering a continuously and/or consecutively received PDCP SDUs tothe upper layer immediately if a PDCP entity receives the PDCP SDUs froma RLC entity through a RLC re-establishment.

-   -   if RSN=LAST+1:        -   deliver to upper layer in ascending order of the associated            SN value:            -   all stored PDCP SDU(s) with consecutively associated SN                value(s)>=RSN;        -   set LAST to the SN of the last PDCP SDU delivered to upper            layers;    -   else if the PDCP SDU received by PDCP is not due to the RLC        re-establishment:        -   deliver to upper layer in ascending order of the associated            SN value:            -   all stored PDCP SDU(s) with an associated SN<RSN;            -   all stored PDCP SDU(s) with consecutively associated SN                value(s)>=RSN;        -   set LAST to the SN of the last PDCP SDU delivered to upper            layers.

According to the above procedure text, when a PDCP SDU is receivedthrough a RLC re-establishment, the present disclosure proposes todetermine whether a sequence number (SN) of received PDCP SDU is equalto LAST+1. Upon the determination, if the sequence number of receivedPDCP SDU is determined to be LAST+1, the received PDCP SDU and any PDCPSDUs having a consecutively in-sequence sequence number after thesequence number of the received PDCP SDU, should immediately deliver toan upper layer in-sequence order rather than storing these into areception buffer.

FIG. 8 is a first exemplary data flow representing a delivery of PDCPdata unit according to the present invention.

As illustrated in FIG. 8, firstly, a PDCP PDU containing a PDCP SUD witha sequence number is received. Here, the sequence number may be definedas ‘RSN’. Thereafter, an operation of a deciphering and a headerdecompression are performed, and then the deciphered and decompressedPDCP SDU is stored in a PDCP buffer. Then, the PDCP entity check whethera RSN is greater than or equal to a NEXT. If the RSN is greater than orequal to the NEXT, the NEXT is set to RSN+1. Thereafter, it isdetermined that whether the sequence number of received PDCP SDU (i.e.,RSN) is equal to LAST+1. Upon the determination, If the RSN is equal toLAST+1, the received PDCP SDU and any PDCP SDUs having a consecutivelyin-sequence sequence number after the sequence number of the receivedPDCP SDU (i.e., all PDCP SDUs with consecutively associated SNvalues >=RSN) are delivered to the upper layer. Thereafter, the PDCPentity sets LAST to the SN of the last PDCP SDU delivered to the upperlayer, and terminates the PDCP SDU delivery procedure. On the otherhand, upon the determination, if the RSN is not equal to LAST+1, then,the PDCP entity determines whether the received PDCP SDU is received dueto the RLC re-establishment. If it is determined that the received PDCPSDU is received due to the RLC re-establishment, the delivery procedureof the PDCP SDU is terminated. If not, the PDCP entity delivers to upperlayer all stored PDCP SDU(s) with an associated SN<RSN in ascendingorder of the associated SN value. Further, the PDCP entity also deliversto upper layer all stored PDCP SDU(s) with consecutively associated SNvalue(s)>=RSN in ascending order of the associated SN value. Thereafter,the PDCP sets LAST to the SN of the last PDCP SDU delivered to the upperlayer, and terminates the PDCP SDU delivery procedure.

Here, a step of determining whether the sequence number of the receivedPDCP SDU is equal to the LAST+1 and a step of determining whether thereceived PDCP SDU is received due to the RLC re-establishment, aremutually exclusive steps. As such, these two determining steps may be inswitched order. Therefore, the following procedure text is also possibleaccording to the present disclosure.

-   -   if the PDCP SDU received by PDCP is not due to the RLC        re-establishment:        -   deliver to upper layer in ascending order of the associated            SN value:            -   all stored PDCP SDU(s) with an associated SN<RSN;            -   all stored PDCP SDU(s) with consecutively associated SN                value(s)>=RSN;        -   set LAST to the SN of the last PDCP SDU delivered to upper            layers.    -   else if RSN=LAST+1:        -   deliver to upper layer in ascending order of the associated            SN value:            -   all stored PDCP SDU(s) with consecutively associated SN                value(s)>=RSN;        -   set LAST to the SN of the last PDCP SDU delivered to upper            layers;

FIG. 9 is a second exemplary data flow representing a delivery of PDCPdata unit according to the present invention.

As illustrated in FIG. 9, a PDCP PDU containing a PDCP SUD with asequence number is received. Here, the sequence number may be defined as‘RSN’. Thereafter, an operation of a deciphering and a headerdecompression are performed, and then the deciphered and decompressedPDCP SDU is stored in a PDCP buffer. Then, the PDCP entity check whethera RSN is greater than or equal to a NEXT. If the RSN is greater than orequal to the NEXT, the NEXT is set to RSN+1. Thereafter, it isdetermined that whether the received PDCP SDU is received due to the RLCre-establishment. If it is determined that the received PDCP SDU isreceived due to the RLC re-establishment, the PDCP entity determineswhether the sequence number of received PDCP SDU (i.e., RSN) is equal toLAST+1. Upon the determination, If the RSN is equal to LAST+1, thereceived PDCP SDU and any PDCP SDUs having a consecutively in-sequencesequence number after the sequence number of the received PDCP SDU(i.e., all PDCP SDUs with consecutively associated SN values >=RSN) aredelivered to the upper layer. Thereafter, the PDCP entity sets LAST tothe SN of the last PDCP SDU delivered to the upper layer, and terminatesthe PDCP SDU delivery procedure. On the other hand, if the RSN is notequal to LAST+1, the delivery procedure of PDCP SDUs is immediatelyterminated. If it is determined that the received PDCP SDU is notreceived due to the RLC re-establishment, the PDCP entity delivers toupper layer all stored PDCP SDU(s) with an associated SN<RSN inascending order of the associated SN value. Further, the PDCP entityalso delivers to upper layer all stored PDCP SDU(s) with consecutivelyassociated SN value(s)>=RSN in ascending order of the associated SNvalue. Thereafter, the PDCP sets LAST to the SN of the last PDCP SDUdelivered to the upper layer, and terminates the PDCP SDU deliveryprocedure.

The COUNT format including the PDCP SN (Sequence Number) referred in thepresent disclosure may also be applied to the present invention. Here,the COUNT value is composed of a HFN (Hyper Frame Number) and the PDCPSN. The length of the PDCP SN may set by an upper layer. The COUNT valuemay be used instead of the PDCP SN, in order to solve a wrap aroundproblem that can be caused during any operation mentioned in the presentdisclosure.

The present disclosure may provide a data communication method in awireless communication system, the method comprising: receiving, from alower layer, a data unit having a sequence number; storing the receiveddata unit in a buffer; determining whether the sequence number of thereceived data unit is equal to a sequence number +1 from a sequencenumber of a last delivered data unit; delivering, in ascending order,all stored data units with consecutively associated sequence numbersgreater than or equal to the sequence number of the received data unitbased on the determining step, and setting a sequence number of a lastdata unit delivered to an upper layer as a ‘LAST’, wherein the lowerlayer is a Radio Link Control (RLC) layer, the steps of determining anddelivering are performed in a Packet Data Convergence Protocol (PDCP)entity, the data unit is a PDCP Service Data Unit (SDU), the data unitis received through a RLC re-establishment, a header decompression or adeciphering is performed between the receiving step and the storingstep, the sequence number +1 indicates a sequence number that isimmediately subsequent to the sequence number of the last delivered dataunit, and the sequence number +1 indicates a next sequence number fromthe sequence number of the last delivered data unit.

Although the present disclosure is described in the context of mobilecommunications, the present disclosure may also be used in any wirelesscommunication systems using mobile devices, such as PDAs and laptopcomputers equipped with wireless communication capabilities (i.e.interface). Moreover, the use of certain terms to describe the presentdisclosure is not intended to limit the scope of the present disclosureto a certain type of wireless communication system. The presentdisclosure is also applicable to other wireless communication systemsusing different air interfaces and/or physical layers, for example,TDMA, CDMA, FDMA, WCDMA, OFDM, EV-DO, Wi-Max, Wi-Bro, etc.

The exemplary embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.).

Code in the computer readable medium may be accessed and executed by aprocessor. The code in which exemplary embodiments are implemented mayfurther be accessible through a transmission media or from a file serverover a network. In such cases, the article of manufacture in which thecode is implemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration without departing from the scope of the presentdisclosure, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

As the present disclosure may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalents of such metes and bounds are therefore intendedto be embraced by the appended claims.

1. A data communication method in a wireless communication system, themethod comprising: receiving, from a lower layer, a data unit having asequence number; storing the received data unit in a buffer; checkingwhether the received data unit is received due to a radio link control(RLC) re-establishment; determining whether the sequence number of thereceived data unit is equal to a sequence number +1 from a sequencenumber of a last delivered data unit, if the received data unit isreceived due to the RLC re-establishment according to the checking step;and delivering, in ascending order, all stored data units withconsecutively associated sequence numbers greater than or equal to thesequence number of the received data unit based on the determining step.2. The method of claim 1, wherein the lower layer is a Radio LinkControl (RLC) layer.
 3. The method of claim 1, wherein the steps ofdetermining and delivering are performed in a Packet Data ConvergenceProtocol (PDCP) entity.
 4. The method of claim 1, wherein the data unitis a PDCP Service Data Unit (SDU).
 5. The method of claim 1, wherein aheader decompression or a deciphering is performed between the receivingstep and the storing step.
 6. The method of claim 1, wherein thesequence number +1 indicates a sequence number that is immediatelysubsequent to the sequence number of the last delivered data unit. 7.The method of claim 1, wherein the sequence number +1 indicates a nextsequence number from the sequence number of the last delivered dataunit.
 8. The method of claim 1, further comprising: setting a sequencenumber of a last data unit delivered to an upper layer as a ‘LAST’.